It is often desired to monitor the blood pressure of a patient to determine the patient's medical condition, and particularly to detect cardiovascular system stress. Blood pressure is often monitored invasively by inserting a catheter into a patient's vein or artery, with the open end of the catheter exposed to the pressure of the patient's circulatory system. The catheter is connected to a fluid line leading from a source of sterile solution that fills the fluid line and catheter. A fluid pressure sensing device, typically a pressure transducer, is connected in fluid communication with the line to sense the patient's blood pressure, which is transmitted by the fluid to the pressure transducer. The pressure transducer varies an electrical signal in proportion to the patient's blood pressure, and the electrical signal is monitored to detect changes in the patient's condition. Typically, a very low flow rate of solution passes through the fluid line and pressure transducer to clear away thrombi and minute air bubbles that would distort the pressure reading.
Blood pressure monitoring apparatus usually include a flush valve, disposed upstream of the pressure transducer, for controlling the rate of fluid flow through the device. The flush valve typically contains a capillary flow passage that restricts flow to a desired low rate. Before the fluid line is first connected to the patient, it is often desirable to greatly increase the flow rate of solution passing through the device to clear the line and device of air. Flush valves generally have a flushing position, bypassing the capillary passage, which permits this greatly increased flow through the device. Flushing is also periodically performed on a momentary basis while the fluid line is connected to the patient to clear thrombi, which may have accumulated within the line and device.
In addition to the flush valve, blood pressure monitoring apparatus may include a flow direction valve, which can be used to select one of three fluid flow conditions: (a) enabling normal flow through the device; (b) shunting fluid from the patient through a vent; and (c) blocking the flow of fluid into the device to prevent the fluid from entering the patient, thereby permitting other medication to be introduced into the catheter or fluid to be withdrawn from the patient through the catheter.
In recent years, apparatus combining a flush valve, a pressure sensing device, and a flow direction valve have been developed in a relatively low cost disposable format, which eliminates the need to sterilize the apparatus for reuse with other patients, and eliminates the risk of transmission of infectious disease caused by improper sterilization. Due to competition between manufacturers, it is desirable for these disposable devices to be as low in cost as possible, yet reliable, compact and simple to use.
Kodama et al., U.S. Pat. No. 4,683,894, discloses a disposable physiological pressure sensing device which attempts to meet these goals. The device includes a conventional three position stop cock valve for flow direction control, a pressure transducer, and a flush valve. The flush valve consists of a cylindrical valve body seated within a pressure chamber and sealed by an O-ring seal. The valve body includes a capillary bore passing through it that restricts fluid flow to a low rate for normal operation. The valve body is withdrawn from the chamber by pressing a lever on the device, which unseats the O-ring seal, and creates a bypass flow passage between the valve body and chamber for greatly increased flushing flow through the device.
While this device is disposable, its manufacture requires the assembly of many parts, raising the per unit cost. Rotation of the stop cock valve to change flow direction is a two-handed operation, which can be awkward for a health professional treating a patient in an emergency medical situation. Additionally, since activating the flush valve creates a bypass passage around the capillary bore formed in the valve body, the capillary bore is not flushed of any air or other contaminants that may be collected therein.
Other conventional blood pressure monitoring apparatus use a flush valve having an elastomeric valve body that is seated within the device, and which restricts normal flow to a capillary passage within the apparatus. The elastomeric valve body is deformed to open a second and larger bypass passage. One example of such a flush valve is shown in von Berg, U.S. Pat. No. 4,696,305, which discloses a device with interconnected parallel flow passages. One flow passage contains a capillary bore for normal flow through the device. The second and larger passage is closed by a thimble-shaped elastomeric valve body located within and sealing that passage. A plunger inserted within the valve body is depressed to open this second or flushing passage, causing the valve body to elongate and narrow to allow fluid flow through the passage. Again, since this device creates a bypass flushing flow, the capillary flow passage is not flushed to clear it of air or other contaminants.